optional template for the start script

Or maybe before/after scripts that are sourced if they exist. Just some way for conscript programs to do stuff outside the JVM if they need to.

Start by tracing how conscript generates and invokes its start script. Compare the requested optional before/after sourced scripts with the existing command lifecycle, then clarify the expected behavior for scripts that need to run outside the JVM. Done should include an agreed lifecycle and coverage for the chosen behavior.

Written by the indexing model from the issue text.